A professor who has accurately predicted the winner in each of the past eight presidential elections announced that his model points to a victory this November for Republican nominee Donald Trump.

Instead of relying on the latest voter polls, Allan Lichtman, a distinguished professor of history at American University, answers 13 true-or-false questions, which he calls “The Keys to the White House.” The questions are written to gauge the performance of the current president’s political party.

If fewer than six answers return false, then the ruling party hangs on for another four years, according to the model. If six answers or more are false, as is the case this year, then the challenging party will win.

The model was first used to predict President Ronald Reagan would win his bid for reelection in 1984. By design, it applies retrospectively for every prior election dating back to Abraham Lincoln’s victory in 1860.

But this could be the year that breaks his model, Lichtman said, citing the unprecedented nature of Mr. Trump’s campaign.

“We’ve never before seen a candidate who’s spent his life enriching himself at the expense of others,” Lichtman said, describing Trump as “a serial fabricator.” Trump’s numerous shocking deeds include inviting a foreign power to interfere in American elections and twice inciting violence against an opponent, Lichtman added.

“Given all of these exceptions that Donald Trump represents, he may well shatter patterns of history that have held for more than 150 years, lose this election even if the historical circumstances favor it,” Lichtman told the Post.

Trump’s departure from historical norms was well-known during the primaries, when fellow Republicans urged him to behave in a more “presidential” fashion, as The Christian Science Monitor’s Linda Feldmann reported in March.

Looking all the way back to the founding of the United States, experts see no one quite like Trump – not even in notoriously brash seventh President Andrew Jackson.

Cal Jillson, a presidential scholar at Southern Methodist University, said Mr. Jackson had “a very individualistic personal style” but saw himself as “first among equals.”

“Trump is different,” Dr. Jillson told the Monitor. “He does not see himself as first among equals, he sees himself as a savior of sorts, as a singular individual.”

Five of the factors underpinning Lichtman’s prediction of a Democratic loss, however, have nothing to do with Mrs. Clinton’s challengers. The loss prediction comes from poor Democratic performance in the midterm election, President Barack Obama's inability to run again, the lack of any major policy change in Mr. Obama’s second term, the absence of major foreign policy successes, and Clinton's lack of charismatic appeal.

The sixth factor working against the Democrats is Libertarian presidential candidate, Gary Johnson.

“One of my keys,” Lichtman explained, “would be that the party in power gets a ‘false’ if a third-party candidate is anticipated to get 5 percent of the vote or more.”

Clinton and Trump are virtually tied ahead of Monday’s presidential debate, the first of the general election, according to Washington Post-ABC News poll numbers published Sunday. Among registered voters, Clinton and Trump are tied at 41 percent, with Mr. Johnson at 7 percent and Green Party candidate Jill Stein at 2 percent.

Among likely voters, Clinton is favored by 46 percent, while 44 percent back Trump, 5 percent support Johnson, and 1 percent are for Dr. Stein.

Americans are open to the idea of voting for a third-party candidate, and this year’s election more than any recent race, “begged for a serious alternative,” Ian Tuttle wrote last month for the National Review, a conservative news and commentary publication that opposes Trump.

“Most Republicans cannot stomach the idea of a Clinton presidency. Most Democrats cannot stomach the idea of a President Trump. Either would be ‘the end of America as we know it,’” Mr. Tuttle, the Thomas L. Rhodes Fellow at the National Review Institute, wrote. Neither Johnson nor Stein had a chance, he noted.

“The loathsomeness of the candidate on one side helped fuel the support of a loathsome candidate on the other side, and box out any serious third-party alternative,” Tuttle wrote.

Then there’s the lingering claim that Trump will see a bump on Election Day unanticipated by the polls because some of his supporters are too shy to admit they support him, as the candidate himself said in June. Politico reported there was no evidence during the primaries that such closeted Trump supporters exist.